The invention relates to a vented dryer having counter-flowing air detection, i.e. detection of an airstream flowing in the opposite direction to the flow direction provided for normal operating conditions (counter-flowing air current), and to a method for the operation of said vented dryer.
In a dryer, in particular a laundry dryer, articles to be dried, in particular laundry, contained in a generally rotating drum are dried by conducting through the drum, and consequently through the articles to be dried, a heated current of air which extracts moisture from the articles to be dried, as a result of which the said damp laundry articles are gradually dried.
The supplied air current (“process air flow”) is heated in a supply line (supply air duct or, in this case, “first process air duct”) upstream of the drum (in the case of a laundry dryer also “laundry drum”) by means of a heating device and after passing through the drum is either discharged to the outside (exhaust air or vented dryer) or conveyed to a heat exchanger in which the air current is cooled down and the moisture extracted from the articles to be dried and entrained in the air current precipitates out as condensate. Hybrid forms hereof are likewise known. A blower (process air blower) is generally used for conveying the air.
In a vented dryer, the moist, warm air coming from the drum is conveyed through an exhaust air outlet into the room where the dryer is installed or via an exhaust air system into the open air. Depending on the weather conditions, in particular the wind conditions, it can happen that air is forced into the vented dryer via the exhaust air outlet. This can lead to a malfunctioning of the system that is typically present in the vented dryer as a protection against overheating. That is to say that in order to protect against overheating there is normally disposed in a vented dryer a temperature sensor or temperature limiter which is positioned in the flow direction of the process air downstream of the heating device and upstream of the drum and which can turn off the heating device if overheating is detected in the vented dryer. If the air flow provided for normal operating conditions is disrupted due to an infiltration of air (counter-flowing air) and the process air flows in a direction opposite to the intended direction, air heated by the heating device can flow in the opposite direction, i.e. away from the drum. This hot air can flow into a supply air duct or, if present, into a recirculated air duct. Usually there is lint present in the recirculated air duct, so under very unfavorable conditions there may be an increased risk of fire. In any case a hot air current in the opposite flow direction can lead to malfunctions and is therefore undesirable.
A second temperature sensor or temperature limiter is generally necessary at the present time in order to prevent overheating of the vented dryer in the event of the occurrence of an air current flowing in the opposite direction.